Surface Deformation on Venus Driven by Downwelling: Results of Scaled Analogue Experiments

Details Surface Deformation on Venus Driven by Downwelling: Results of Scaled Analogue Experiments Surface Deformation on Venus Driven by Downwelling: Results of Scaled Analogue Experiments

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.p51b1201c&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #P51B-1201

Mathematics

Logic

8120 Dynamics Of Lithosphere And Mantle: General (1213)

Scientific paper

Tessera terrains and large basins on Venus and their corresponding gravity fields have been hypothesized to form by interaction between mantle downwellings and the Venusian lithosphere. Scaled analogue experiments have been carried out to model this type of interaction. Mantle downwellings are simulated by a Rayleigh- Taylor instability that is initiated by a hemispherical perturbation in the upper part of the model asthenosphere. Once initiated the resulting flow draws the overlying ductile mantle lithosphere, lower crust and brittle upper crust of the models towards the locus of the downwelling. Preliminary experiments investigate the effects of Rayleigh-Taylor initiator geometry and crustal rheology. More complex experiments subsequently explore deformation of a density and rheologically layered Venusian lithosphere. The experimental asthenospheric mantle is made of a transparent silicone polymer with viscosity that scales to 1021 Pa.s. The density difference that drives the mantle downwelling scales to 300 kg/m3. Progress of mantle downwellings and surface deformation in the models are monitored by time-lapse photography. A laser scanning system maps the model surface topography. In response to mantle downwelling, lithosphere models with rheological and density stratification scaled to a basaltic Venusian lithosphere develop surficial basins with depths that scale to those observed on Venus. Large-scale folding and compression, followed by plateau formation that is related to isostatic equilibration following cessation of the downwelling are also observed in certain experiments. However, the results also suggest that large, uplifted and highly deformed regions of Venus (tesserae) may not be constructed of basaltic crust, since plateaus formed in the models fail to achieve similar scaled heights. Further work is required to evaluate similar models with crustal densities scaled to crust of more felsic compositions.

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